Destroy all testenv domains

Leaving these running with IP's from previous test runs may cause IP
conflicts and end up in errors booting new instances in devtest runs.
Killing these vm's is only needed while using nova-baremetal as ironic
will assert their state.

Ideally this wouldn't live in boot-seed-vm but its where we currently
kill the seed so it makes sense to keep it together.

Change-Id: I591775f85169d1c454373b19d3a66ba80bf818d3
Merge "Destroy all testenv domains"